Are you going to sell all your DVD's on Ebay & get everything on Blu-Ray?
Keep your DVD's & Only buy new movies on Blu-Ray.
Buy a few select titles that you already own on Blu-Ray & get all the new releases on Blu-Ray .
or only buy select titles on Blu-Ray & still get most of my movies on DVD.

I don't have a large DVD collection (around 300 movies) I only bought movies that I knew I'd like & would watch multiple times but I'll be keeping all my old DVD's (I only bought wide screen versions even before I had a widescreen TV) But I will buy my favorite movies again (about 20 titles total) & after that all my new movies will be Blu-Ray.
I haven't bought a DVD since I got my Playstation 3.

I have about 350 DVD movie (give or take) in my collection right now and I have not bought any since I have purchased the Playstation 3 back in December. I have only 10 Blu-Ray movies so far. I have bought some new releases and have replaced some of my existing movies in my DVD collection. I just give my old DVD's that were replaced to my friends for free. I plan on replacing more of my DVD movie with BLu-Ray and continue to buy new releases.

I have about forty or more Blu-ray and HD DVD's and try to only buy in these formats now, especially as Amazon sells them so cheaply. I too give away many of my older discs, except I will always keep Piartes Dead Mans Chest as the best Blu-ray to SD DVD demo! That one got several friends to go Blu!